The invention relates to a portable ID transmitter for an authentication system and a method for operating the authentication system. In particular, the invention refers to an authentication system with which a portable ID transmitter can be authenticated to the vehicle to enable vehicle functions for an operator carrying the portable ID transmitter.
In prior art, different so-called keyless access systems are disclosed. They are based on radio communication between a vehicle infrastructure and a portable ID transmitter. In the context of the radio communication carried out, the desired authentication is performed, for example, by exchanging and checking encrypted authorization data.
The use of low-frequency (LF) and high-frequency (HF) radio waves is known and widely used in keyless access systems. In prior art, combined communication using LF/HF systems has also been disclosed.
With radio-based authorization systems, security, especially against compromising the radio communication carried out, is of decisive importance. When releasing a vehicle function using portable ID transmitters, the determination of a position, a distance, or a similar quantity, for example, to check the plausibility of bidirectional communication, is known from prior art. For example, it is known to evaluate the signal strength of an LF radio communication between a portable ID transmitter and a vehicle authentication system. A supplementary or alternative concept to increase security against compromise can simply be based on limiting the transmission power of an LF communication. By limiting the transmission power of an LF communication between vehicle and ID transmitter, it is ensured that, for example, an LF alert signal transmitted from the vehicle to the ID transmitter can only be received by the other communication partner if a maximum distance between ID transmitter and vehicle is not exceeded.
Many of the well-known authentication systems still have the fundamental disadvantage that an LF radio communication or an HF radio communication can be extended, for example, in the context of so-called relay station attacks. To avoid such or other compromises, countermeasures are necessary some of which, however, are quite costly.
Therefore, it is the objective of the invention to improve the well-known authentication methods so that they provide an effective, but at the same time comparatively inexpensive protection against a compromise of the transmitted signals.